Smoking and plasma fibrinogen, lipoprotein (a) and serotonin are markers for postoperative infrainguinal graft stenosis.

OBJECTIVES: A number of systemic variables are associated with infrainguinal graft failure and also with experimental smooth muscle hyperplasia. Stenosis is the most common cause of infrainguinal graft thrombosis but it is not known if systemic variables are associated with stenosis. DESIGN, MATERIALS, AND METHODS: In this study, clinical and serological factors were measured and correlated with stenosis development in 81 infrainguinal bypass grafts (52 vein, 29 PTFE; 28 with stenosis) in prospective (n=46) and retrospective (n=35) groups. Pre-existing stenosis was excluded by perioperative graft assessment. RESULTS: There was a significantly greater proportion of smokers in the patients who developed stenosis (11/18; 61%) compared with those who did not (6/28; 21%, p=0.006; chi 2). Patients who developed stenosis also had significantly (Mann Whitney U-tests), higher circulating levels of [median (interquartile range)] fibrinogen (412.5 (356-484.5) vs. 339 (300-397.7) mg/100ml, p=0.003), Lipoprotein (a) (0.20 (0.05-0.45) vs. 0.085 (0.05-0.23) g/l, p=0.03) and 5-hydroxytryptamine (14.1 (6.6-45) vs. 4.41 (3-8.39) nmol/l, p=0.005), than those without stenosis. By logistic regression, these associations were independent of graft material and whether grafts were studied prospectively or retrospectively. CONCLUSIONS: Smoking and plasma fibrinogen, Lp(a) and 5-hydroxytryptamine are markers for postoperative infrainguinal graft stenosis.

Naftidrofuryl inhibits the release of 5-hydroxytryptamine and platelet-derived growth factor from human platelets.

Angioplasty and bypass-grafting are associated with restenosis which limits their efficacy. Platelet-rich thrombus formation is the predominant cause of acute occlusion whereas platelet release products with proliferating properties, e.g. 5-hydroxytryptamine (5-HT) and platelet-derived growth factor (PDGF), may contribute to late restenosis. Naftidrofuryl (NAF), a drug for the treatment of peripheral vascular disease, was shown previously to inhibit platelet shape change and aggregation. This study establishes whether NAF inhibits the release of 5-HT and PDGF from platelets obtained from healthy subjects. Platelets stimulated with agonists aggregated less and released less 5-HT/PDGF when pre-incubated with NAF. Indomethacin (INDO), a cyclooxygenase inhibitor, alone inhibited aggregation and PDGF/5-HT release; NAF enhanced the inhibitory effects of INDO. The effect of NAF, on its own or in combination with a cyclooxygenase inhibitor, may therefore confer protection against graft occlusion.

Hypothermia-induced Haemostatic and Biochemical Phenomena. An Experimental Model.

Hypothermia (24°C) was induced in 7 healthy male dogs. Hematological, hemostatic and biochemical parameters were evaluated before the onset and after 3 h of hypothermia. Following hypothermia, there was a significant increase in red cell count, hematocrit and haemoglobin concentration. The white cell and platelet counts were decreased significantly and the mean platelet volume increased significantly. The activated partial thromboplastin time was significantly prolonged whereas the prothrombin time was unchanged. Associated with these changes there was a significant increase in serum glucose and a small increase in aspartate transaminase activity probably due to muscle leakage. No change occurred in the more liver-specific alanine transaminase. The arterial pH decreased and the changes in gasses observed as a result of hypothermia were compatible with a mixed respiratory-metabolic acidosis. The mean aortic blood pressure also dropped markedly. The hematological and hemostatic changes suggest that widespread tissue 'injury' occurs even in short term hypothermia with platelet activation and accumulation in the liver and spleen. This model of hypothermia may be of use in the study of the thrombotic diathesis observed in this condition and serve as a test bed for drugs of potential use in conditions such as Raynaud's syndrome and hypothermic surgery (e.g. coronary artery bypass).

Serotonin, histamine and platelets in vascular disease with special reference to peripheral vascular disease

Cardiovascular disease is a major cause of death. There is evidence that this disease is predicted and its progression influenced by various factors (e.g. hyperlipidaemia). In this review, we consider aspects of platelet structure and function which may explain how this cell type contributes to the pathogenesis of vascular disease. The platelet also contains bioamines (serotonin, 5-HT; histamine) which are potent vasoactive substances. Studies involving patients with peripheral vascular disease (PVD) where abnormalities in platelet function (platelet aggregation and platelet shape change) and in bioamine status (vascular, platelet and plasma bioamine concentrations) are reviewed. We also discuss how platelet activation (in vitro) and plasma lipids influence intraplatelet bioamine status. Finally, we report in vitro evidence of the effect of two drugs prescribed to PVD patients: aspirin and naftidrofuryl. Aspirin is an ineffective inhibitor of 5-HT-induced whole blood platelet aggregation whereas naftidrofuryl is effective in the presence or absence of aspirin. By identifying and altering the factors which contribute to the pathogenesis of atherosclerosis we will be better equipped to prevent, reverse or retard this process

The effect of a slow release formulation of bezafibrate on lipids, glucose homeostasis, platelets and fibrinogen in type II diabetics: a pilot study.

A double-blind placebo-controlled prospective trial assessed the effect of a slow release formulation of bezafibrate (Bezalip Mono) on lipids, glucose homeostasis, platelet function and plasma fibrinogen in non-insulin dependent (type II) diabetics. Twenty-four patients completed the trial. There was a significant improvement in the cholesterol and triglyceride levels and in the fasting blood glucose and glycated haemoglobin levels of those who received the active preparation but not in those who received placebo. Treatment, but not placebo, also resulted in a significant fall in plasma fibrinogen concentration and a trend towards inhibition of platelet aggregation. Bezafibrate was well tolerated and only one patient withdrew from the trial possibly because of side-effects of the drug. A larger study is needed to establish whether bezafibrate can reduce non-lipid risk factors (e.g., plasma fibrinogen concentration; glucose intolerance--hyperinsulinaemia) in normo- and hyperlipidaemic patients.

Platelet abnormalities in patients with cystic fibrosis and obligate heterozygotes.

Following our previous report that thrombocytosis and platelet hyperaggregability (as tested in platelet rich plasma) occur in patients with cystic fibrosis (CF), we have now examined whether this thrombocytosis is related to leukocytosis, and whether platelet hyperaggregability can be documented in whole blood using impedance aggregometry. Our observations show that platelet counts are related to white cell counts (r = 0.34; p = 0.001) and that therefore thrombocytosis may be part of a secondary response to bronchopulmonary infection, which is characteristic of these patients. Platelet counts were, however, not related to serum iron concentration despite the finding of varying degrees of iron deficiency in approximately 50% of patients with cystic fibrosis. Whole blood aggregometry demonstrated platelet hyperaggregability in patients with cystic fibrosis independently of platelet counts. Platelet aggregation (in platelet rich plasma and in whole blood) was normal in obligate heterozygotes, thus suggesting that platelet hyperaggregability in CF is not a consequence of abnormal genetic information.

ADPase activity in human maternal and cord blood: possible evidence for a placenta-specific vascular protective mechanism.

ADPase enzyme activity was assessed in maternal and cord plasma by adding radiolabelled ADP and quantitating the degradation products. Cord plasma had sufficiently greater ADPase activity than the corresponding maternal plasma obtained ante- and post-partum. Thus, residual radiolabelled ADP was 30, 32 and 17% of total radioactivity after 30 min incubation (37 degrees C) in maternal ante-partum, maternal post-partum and cord plasmas, respectively. ADPase may act as a platelet aggregation inhibitor in the placental and fetal circulation.

86Rb(K) influx and [3H]ouabain binding by human platelets: evidence for beta-adrenergic stimulation of Na-K ATPase activity.

Although active transport of potassium into human platelets has been demonstrated previously, there is hitherto no evidence that human platelets have an ouabain-inhibitable Na-K ATPase in their membrane. The present study demonstrates active rubidium (used as an index of potassium influx), 86Rb(K), influx into platelets, inhibitable by ouabain, and also demonstrates the presence of specific [3H]ouabain binding by the human platelet. This 86Rb(K) influx was stimulated by adrenaline, isoprenaline, and salbutamol, but noradrenaline caused a mild inhibition. Active 86Rb(K) influx by platelets was inhibited markedly by timolol, mildly by atenolol, but not by phentolamine. Therefore, active 86Rb(K) influx in human platelets is enhanced by stimulation of beta adrenoceptors of the beta 2 subtype. The platelet may therefore replace the leukocyte in future studies of Na-K ATPase activity. This would be a considerable advantage in view of the ease and rapidity of preparation of platelets.

Iron chelators inhibit human platelet aggregation, thromboxane A2 synthesis and lipoxygenase activity.

The iron chelators desferrioxamine and 1,2-dimethyl-3-hydroxypyrid-4-one (L1) inhibited human platelet aggregation in vitro as well as thromboxane A2 synthesis and conversion of arachidonate to lipoxygenase-derived products. Non-chelating compounds related to L1 were without effect on cyclooxygenase or lipoxygenase activity. Since both cyclooxygenase and lipoxygenase are iron-containing enzymes, it is suggested that the inhibition of platelet function by these iron chelators may be related to the removal or binding of iron associated with these enzymes. These iron chelators may therefore be of potential therapeutic value as platelet antiaggregatory agents and of possible use in the treatment of atherosclerotic and inflammatory joint diseases.

Dietary fish oil supplements preserve renal function in renal transplant recipients with chronic vascular rejection.

The effect of dietary fish oil supplements on renal failure and lipid abnormalities was studied in 14 adult renal transplant recipients with chronic vascular rejection. The rate of decline of renal function (assessed by studying the slope of reciprocal plasma creatinine plots) slowed significantly during a 6-month period on fish oil supplements compared with the preceding 6-month control period (slope 1/cr during supplementation -3.6 X 10(-5) mumols/l per month compared with -13.5 X 10(-5) before, the difference in slope being -9.8 X 10(-5), 95% confidence interval (CI) -16.2 X 10(-5), -3.5 X 10(-5), P less than 0.05). Total plasma triglyceride concentrations decreased during supplementation (mean change -1.15 mmol/l, 95% CI -1.84, -0.47, P less than 0.003), but there was no change in total plasma cholesterol concentration or urinary protein excretion. Platelet function was studied in nine patients. Platelet aggregation induced by adrenaline and collagen was reduced by fish oils (median change in per cent aggregation), adrenaline 2 mumols/l, -36% (95% CI -68%, -8%, P less than 0.05), collagen 1 mg/1, -13% (95% CI -44%, -2%, P less than 0.05). Platelet thromboxane A2 release in response to these agents was also significantly reduced. These results demonstrate that fish oils preserve residual function in renal graft failure due to chronic vascular rejection.

Effect of heparin and contrast medium on platelet function during routine cardiac catheterisation.

Platelet function was studied during coronary angiography of patients complaining of chest pain. The following changes occurred 5 min after injecting 100 IU.kg-1 body weight of a conventional high molecular weight heparin: (a) a significant fall in platelet count; (b) a significant enhancement of platelet aggregation in platelet rich plasma (turbidometric technique) and in whole blood (platelet aggregation technique); and (c) significantly enhanced release of platelet thromboxane A2, a vasoconstrictor. These changes tended to reverse towards baseline values 5 min after injecting a contrast medium (Conray 420), which was found to inhibit platelet aggregation. Thus heparinisation with a high molecular weight heparin seems to cause pronounced activation of platelets in patients undergoing coronary angiography, and this may contribute to the pathogenesis of cardiac ischaemia that may occur during this procedure. Since coronary artery bypass surgery in similar patients involves the use of heparin at much higher doses without the concomitant use of an antiaggregatory contrast medium, it is possible that platelet hyperaggregability may contribute to the well documented ischaemic brain injury associated with this form of surgery. Furthermore, the use of high molecular weight heparin after successful coronary angioplasty or thrombosis may influence the incidence of reocclusion. These findings therefore suggest that low molecular weight heparinoids should be evaluated in these situations since these anticoagulants are only weak activators of platelet aggregation.

Platelet hyperaggregability in cystic fibrosis.

Platelet function was investigated in 15 patients with cystic fibrosis (CF) and in ten age-matched controls. Marked hyperaggregability of platelets to adrenaline, collagen and arachidonic acid was observed in platelet rich plasma (PRP) prepared from patients with cystic fibrosis. Thromboxane A2 (TXA2) release from these platelets was also markedly enhanced. Hyperaggregability and increased TXA2 release observed in patients with CF was not due to the higher platelet counts in these patients since hyperaggregability was observed even in those patients whose platelet counts were similar to those in controls. Platelet hyperaggregability and increased thromboxane release in these patients were also independent of their body weight and occurred despite supplementation with vitamin E. Hyperaggregability of platelets in CF may be clinically relevant since it may contribute to the pathogenesis of bronchoconstriction through the release of TXA2 and other bronchoconstrictor platelet products such as serotonin.

The effect of non-esterified fatty acids on vascular ADP-degrading enzyme activity.

Following our observations that non-esterified fatty acids (NEFAs) inhibit prostacyclin (PGI2) synthesis and accelerate PGI2 degradation, we have examined the possibility that NEFAs may also affect the activity of vascular ADPase, which converts the platelet pro-aggregatory adenosine diphosphate (ADP) to adenosine, an inhibitor of aggregation and a vasodilator. Incubation, in buffer solutions, of NEFAs with intact rat aortic rings significantly inhibited vascular ADPase activity. This inhibition was more marked at higher NEFA concentrations and with unsaturated fatty acids (linoleic, oleic) than with a saturated fatty acid (stearic). This NEFA-mediated inhibition of vascular ADPase activity could be prevented by the prior addition of fatty acid-free human albumin to the incubate. Similarly, the vascular rings recovered from NEFA-mediated inhibition by washing and further incubation in NEFA-free buffer. Therefore, elevated NEFA concentrations inhibit, reversibly, an enzyme system which is thought to protect the vascular endothelium. The NEFA-mediated inhibition of ADPase activity was also confirmed following incubation of rat aortic rings in human serum enriched with exogenous NEFA. These findings provide further evidence that NEFAs may contribute to the pathogenesis of vascular disease associated with diabetes mellitus and of other conditions where an elevation of serum NEFA concentrations occurs.

Platelet function defects in chronic alcoholism.

Platelet function in alcoholic patients was assessed on admission and during abstinence in hospital. On admission platelets from these patients were significantly less responsive (percentage aggregation and thromboxane A2 release) to conventional in vitro aggregating agents (adrenaline, adenosine diphosphate, and collagen) than platelets from healthy, moderate drinkers. Initially, platelet counts in platelet rich plasma tended to be low and the Simplate II bleeding times frequently prolonged. Platelet aggregation and thromboxane A2 release, however, were inhibited even in patients with normal platelet counts on admission. Platelet aggregation and thromboxane A2 release returned to normal or became hyper-responsive during two to three weeks of abstinence. Platelet counts rose during this period, the largest responses occurring in those patients with the lowest counts on admission. Bleeding times reverted to normal during abstinence and correlated significantly with changes in platelet aggregation, thromboxane A2 release, and platelet count and with the estimated ethanol consumption during the week before admission. Chronic, heavy alcohol ingestion evidently exerts an inhibitory effect on platelet function even in the absence of alcohol in the blood, and this phenomenon is reversible on abstaining. The impaired platelet function, together with the reduced platelet count, may contribute to the bleeding diathesis associated with chronic alcoholism and to the increased incidence and recurrence of gastrointestinal haemorrhage associated with excessive alcohol intake.